In 1946 a Douglas design was beaten by the Vought V-346 proposal (later the F7U Cutlass) for a carrierborne interceptor capable of reaching a speed of 521 kt (600 mph; 966 km/h) at 40,000 ft (12190 m). In 1947 the US Navy launched another design competition for a carrierborne interceptor offering an exceptional climb rate through the use of a delta or modified delta planform drawing on German research in World War II. Douglas evolved a simple basic design with a wing of delta planform, and in June 1947 the US Navy contracted with the company for the preliminary design phase, which resulted in the evolution of the original delta-winged concept into a modified delta type with a mid-set wing.
This wing had considerable sweep, rounded tips, two elevons on each trailing edge and, between the elevons and jetpipe, two pitch-trimming surfaces. The selected engine was the apparently very promising Westinghouse J40 axial-flow turbojet unit on which many other naval warplanes were being based, and provision was made for an afterburning version of engine to provide marginally supersonic speed in level flight as well as a climb to 40,000 ft (12190 m) faster than that of any current fighter, the object being the interception of nuclear-armed attack warplanes before they reached the point at which they could launch their weapons against any US carrier-based battle group. The engine was located in the rear of the fuselage between the swept vertical tail surface and the two wing-root inlets, which were placed just behind the high-set cockpit and nose unit of the tricycle landing gear. The landing gear’s three main units were supplemented by a retractable tail bumper wheel that was required to prevent damage to the underside of the rear fuselage at take-off.
Disastrous J40 engine
In December 1948 the US Navy ordered two XF4D-1 prototypes of this Douglas design. Prototype construction was slow, but even so outpaced that of the XJ40-WE-6 engine, rated at 7,000 lb st (31.14 kN) dry. Eventually the first XF4D-1 took to the air for its maiden flight on 23 January 1951 with the powerplant of one Allison J35-A-17 axial-flow turbojet engine rated at 5,000 lb st (22.24 kN) dry. The second prototype followed with the same type of Allison engine, whose low power prevented any exploration of the new aeroplane’s high-speed performance, but both aircraft were later re-engined first with the XJ40-WE-6 non-afterburning engine and then with the XJ40-WE-8 afterburning engine. With the latter engine the XF4D-1 captured the world absolute speed record, reaching an average speed of 653.88 kt (752.94 mph; 1211.49 km/h), but the engine was then cancelled because of its protracted development problems.
Douglas had foreseen this problem, and was able to revise its design to allow use of another and altogether more effective turbojet engine, the Pratt & Whitney J57 axial-flow unit which was not only more reliable but also more powerful. In March 1953 the Skyray was ordered into production as the F4D-1 with the J57-P-2 engine. The first of these fighters flew in June 1954, exceeding Mach 1 in the course of this initial flight. Despite the high speed reached by the first production machine, the airframe and engine were not well matched and the type’s service debut was delayed by the need to revise the geometry of the inlets, to introduce boundary-layer splitter plate ahead of each inlet, and to modify the fairing round the afterburner installation.
Thus the F4D-1 entered service only in April 1956, and was generally known as the ‘Ford’. Thereafter the type proved effective and popular, being especially notable for its high speed, excellent rate of climb, and outstanding manoeuvrability. Production ended in December 1958 with the delivery of 419 aircraft. The surviving examples of this sole production model received the revised designation F-6A in 1962, and at a time of rapid aeronautical development enjoyed only a short first-line career. The US Navy and US Marine Corps retired their last operational Skyray fighters in February 1964, though the last aircraft were not phased out of service with the US Naval Test Pilot School until December 1969.
Douglas F4D-1 Skyray
Type: carrierborne and land-based interceptor and fighter-bomber
Accommodation: pilot on a Douglas Escapac ejection seat in the enclosed cockpit
Fixed armament: four 20-mm M12 fixed forward-firing cannon with 70 rounds per gun in the leading edges of the wing
Disposable armament: up to 4,000 lb (1814 kg) of disposable stores carried on seven hardpoints (one under the fuselage rated at 1,000 lb/454 kg, and six under the wing with the two units of the central pair each rated at 1,000 lb/454 kg and the four units of the innermost and outermost pair each at 500 lb/227 kg), and generally comprising AAM-N-7 (from 1962 AIM-9) Sidewinder short-range AAMs, 1,000- and 500-lb (454- and 227-kg) free-fall bombs, and multiple launchers each carrying seven or 19 2.75-in (70-mm) air-to-surface unguided rockets
Equipment: communication and navigation equipment, plus APQ-50A search and target-acquisition radar, a gyro weapons sight and Aero 13F fire-control system
Powerplant: one Pratt & Whitney J57-P-2 axial-flow turbojet engine rated at 9,700 lb st (43.15 kN) dry and 14,800 lb st (65.83 kN) with afterburning or, in later aircraft, one Pratt & Whitney J57-P-8, -8A or -8B axial-flow turbojet engine rated at 10,200 lb st (45.37 kN) dry and 16,000 lb st (71.17 kN) with afterburning
Internal fuel: 640 US gal (532.9 Imp gal; 2422.6 litres)
External fuel: up to 600 US gal (499.6 Imp gal; 2271.25 litres) in two 300 or 150 US gal (249.8 or 124.9 Imp gal; 1135.6 or 567.8 litre) drop tanks; no provision for inflight refuelling
Dimensions: span 33 ft 6 in (10.21 m); area 557.00 sq ft (51.75 m²); length 45 ft 3 in (13.79 m); height 13 ft 0 in (3.96 m)
Weights: empty 16,667 lb (7560 kg) basic; normal take-off 22,648 lb (10273 kg); maximum take-off 27,116 lb (12300 kg) or 28,000 lb (12701 kg) overload
Performance: maximum speed 627 kt (722 mph; 1162 km/h) at sea level declining to 604 kt (695 mph; 1118 km/h) or Mach 1.05 at 36,000 ft (10975 m); cruising speed 452 kt (520 mph; 837 km/h) at optimum altitude; initial climb rate 18,300 ft (5578 m) per minute; climb to 49,200 ft (14995 m) in 2 minutes 30 seconds; service ceiling 55,000 ft (16765 m); maximum range 1,042 nm (1,200 miles; 1931 km) with drop tanks; typical range 608 nm (700 miles; 1127 km) with standard fuel; endurance 45 minutes on an interception mission